PROJECT SUMMARY/ABSTRACT Stagnant survival and relapse rates for adolescents and young adults (AYA) with cancer are partially attributed to a modifiable health behavior?suboptimal cancer treatment adherence. Yet, effective interventions are lacking. Aligned with priorities of the NCI and other federal agencies, the long-term objective of this K08 application is to help resolve disparities in cancer treatment outcomes in AYA by targeting nonadherence to life-saving cancer treatments. The goal of this proposal is to employ novel real time mobile health methodologies to examine and intervene on the time-varying, contextual factors that influence AYA adherence to an oral chemotherapy called 6-mercaptopurine, which must be taken daily in the maintenance phase to prevent relapse. In Aim 1, the PI and her mentorship team will determine the temporal associations between time-varying contextual factors (such as fatigue, motivation) and daily 6-mercaptopurine adherence. This Aim will utilize a 6-month intensive longitudinal design that employs bursts of mobile-based ecological momentary assessment with AYA patients and their caregivers (n=30 pairs). In Aim 2, the investigative team will begin to develop a just-in-time adaptive mobile intervention, designed to promote 6-mercaptopurine adherence in this population, by developing contextually-tailored mobile messages and decision rules about the conditions under which to deliver the messages. Just-in-time mobile interventions are well-suited to address limitations of previous interventions by providing personalized adherence support, at the right time, only when it is needed. The creation of messages and decision rules will follow a rigorous mobile health development approach by iteratively incorporating self-management theory, empirical evidence, expert input, and stakeholder feedback. Focus groups with 15 AYA from Aim 1 will be conducted to user-test and refine the messages. In Aim 3, the just-in-time adaptive mobile intervention called AYA ADAPTS (Adherence Assessments and Personalized Timely Support) will be pilot tested in a micro-randomized trial with 30 newly recruited patients. AYA ADAPTS will integrate the tailored mobile messages and decision rules developed and refined in Aim 2. The research team will determine the feasibility and acceptability of this intervention in preparation for the PI's larger-scale optimization trial (R01 proposal). This proposal has methodological, theoretical, clinical, and technological innovations. The research and career development plan, supported by a multi-disciplinary team of experts in a rich academic environment, will support the PI's transition to an independent clinician-scientist who possesses the skills and expertise to use cutting-edge mobile health methods to design the most potent adherence- promotion interventions for pediatric cancer patients. This K08 will provide opportunities to acquire skills and knowledge in: (1) ecological momentary assessment and multi-level statistics, (2) behavior change intervention development applied to mobile health, and (3) the conduct of clinical trials and intervention dissemination and implementation.